我在一个文件中有一个大的位图(比如3888x2592)。现在，我想将位图大小调整为800x533，并将其保存到另一个文件中。
我通常通过调用bitmap来缩放位图。createBitmap方法，但它需要一个源位图作为第一个参数，我不能提供，因为加载原始图像到位图对象当然会超过内存(例如，见这里)。
我也不能读取位图，例如，BitmapFactory.decodeFile(文件，选项)，提供BitmapFactory.Options。inSampleSize，因为我想把它调整到精确的宽度和高度。使用inSampleSize将位图大小调整为972x648(如果我使用inSampleSize=4)或778x518(如果我使用inSampleSize=5，这甚至不是2的幂)。
我还希望避免在第一步中使用inSampleSize读取图像，例如，在第一步中使用972x648，然后在第二步中将其大小调整为800x533，因为与直接调整原始图像的大小相比，质量会较差。
总结一下我的问题:
是否有一种方法来读取一个10MP或更多的大图像文件，并将其保存到一个新的图像文件，调整到一个特定的新宽度和高度，而不得到OutOfMemory异常?
我还尝试了BitmapFactory.decodeFile(文件，选项)和设置选项。out theight and Options。outidth值手动为800和533，但它不是这样工作的。
上面的代码更简洁一些。InputStreams最终关闭了包装，以确保它们也被关闭:
*请注意
输入:InputStream is, int w, int h
输出:位图
try
{
final int inWidth;
final int inHeight;
final File tempFile = new File(temp, System.currentTimeMillis() + is.toString() + ".temp");
{
final FileOutputStream tempOut = new FileOutputStream(tempFile);
StreamUtil.copyTo(is, tempOut);
tempOut.close();
}
{
final InputStream in = new FileInputStream(tempFile);
final BitmapFactory.Options options = new BitmapFactory.Options();
try {
// decode image size (decode metadata only, not the whole image)
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(in, null, options);
}
finally {
in.close();
}
// save width and height
inWidth = options.outWidth;
inHeight = options.outHeight;
}
final Bitmap roughBitmap;
{
// decode full image pre-resized
final InputStream in = new FileInputStream(tempFile);
try {
final BitmapFactory.Options options = new BitmapFactory.Options();
// calc rought re-size (this is no exact resize)
options.inSampleSize = Math.max(inWidth/w, inHeight/h);
// decode full image
roughBitmap = BitmapFactory.decodeStream(in, null, options);
}
finally {
in.close();
}
tempFile.delete();
}
float[] values = new float[9];
{
// calc exact destination size
Matrix m = new Matrix();
RectF inRect = new RectF(0, 0, roughBitmap.getWidth(), roughBitmap.getHeight());
RectF outRect = new RectF(0, 0, w, h);
m.setRectToRect(inRect, outRect, Matrix.ScaleToFit.CENTER);
m.getValues(values);
}
// resize bitmap
final Bitmap resizedBitmap = Bitmap.createScaledBitmap(roughBitmap, (int) (roughBitmap.getWidth() * values[0]), (int) (roughBitmap.getHeight() * values[4]), true);
return resizedBitmap;
}
catch (IOException e) {
logger.error("Error:" , e);
throw new ResourceException("could not create bitmap");
}
承认到目前为止另一个很好的答案，我所见过的最好的代码是在拍照工具的文档中。
请参阅“解码缩放图像”一节。
http://developer.android.com/training/camera/photobasics.html
它提出的解决方案是一个调整大小然后缩放的解决方案，就像这里的其他解决方案一样，但它非常简洁。
为了方便起见，我复制了下面的代码作为一个现成的函数。
private void setPic(String imagePath, ImageView destination) {
int targetW = destination.getWidth();
int targetH = destination.getHeight();
// Get the dimensions of the bitmap
BitmapFactory.Options bmOptions = new BitmapFactory.Options();
bmOptions.inJustDecodeBounds = true;
BitmapFactory.decodeFile(imagePath, bmOptions);
int photoW = bmOptions.outWidth;
int photoH = bmOptions.outHeight;
// Determine how much to scale down the image
int scaleFactor = Math.min(photoW/targetW, photoH/targetH);
// Decode the image file into a Bitmap sized to fill the View
bmOptions.inJustDecodeBounds = false;
bmOptions.inSampleSize = scaleFactor;
bmOptions.inPurgeable = true;
Bitmap bitmap = BitmapFactory.decodeFile(imagePath, bmOptions);
destination.setImageBitmap(bitmap);
}
这可能对其他研究这个问题的人有用。我重写了Justin的代码，以允许该方法也接收所需的目标大小对象。这在使用Canvas时工作得非常好。所有的功劳都应该归于JUSTIN的出色的初始代码。
private Bitmap getBitmap(int path, Canvas canvas) {
Resources resource = null;
try {
final int IMAGE_MAX_SIZE = 1200000; // 1.2MP
resource = getResources();
// Decode image size
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(resource, path, options);
int scale = 1;
while ((options.outWidth * options.outHeight) * (1 / Math.pow(scale, 2)) >
IMAGE_MAX_SIZE) {
scale++;
}
Log.d("TAG", "scale = " + scale + ", orig-width: " + options.outWidth + ", orig-height: " + options.outHeight);
Bitmap pic = null;
if (scale > 1) {
scale--;
// scale to max possible inSampleSize that still yields an image
// larger than target
options = new BitmapFactory.Options();
options.inSampleSize = scale;
pic = BitmapFactory.decodeResource(resource, path, options);
// resize to desired dimensions
int height = canvas.getHeight();
int width = canvas.getWidth();
Log.d("TAG", "1th scale operation dimenions - width: " + width + ", height: " + height);
double y = Math.sqrt(IMAGE_MAX_SIZE
/ (((double) width) / height));
double x = (y / height) * width;
Bitmap scaledBitmap = Bitmap.createScaledBitmap(pic, (int) x, (int) y, true);
pic.recycle();
pic = scaledBitmap;
System.gc();
} else {
pic = BitmapFactory.decodeResource(resource, path);
}
Log.d("TAG", "bitmap size - width: " +pic.getWidth() + ", height: " + pic.getHeight());
return pic;
} catch (Exception e) {
Log.e("TAG", e.getMessage(),e);
return null;
}
}
Justin的代码非常有效地减少了使用大型位图的开销。
在阅读了这些答案和android文档后，以下是调整位图大小的代码，而无需将其加载到内存中:
public Bitmap getResizedBitmap(int targetW, int targetH, String imagePath) {
// Get the dimensions of the bitmap
BitmapFactory.Options bmOptions = new BitmapFactory.Options();
//inJustDecodeBounds = true <-- will not load the bitmap into memory
bmOptions.inJustDecodeBounds = true;
BitmapFactory.decodeFile(imagePath, bmOptions);
int photoW = bmOptions.outWidth;
int photoH = bmOptions.outHeight;
// Determine how much to scale down the image
int scaleFactor = Math.min(photoW/targetW, photoH/targetH);
// Decode the image file into a Bitmap sized to fill the View
bmOptions.inJustDecodeBounds = false;
bmOptions.inSampleSize = scaleFactor;
bmOptions.inPurgeable = true;
Bitmap bitmap = BitmapFactory.decodeFile(imagePath, bmOptions);
return(bitmap);
}
我使用Integer。numberOfLeadingZeros计算最佳样本量，性能更好。
kotlin完整代码:
@Throws(IOException::class)
fun File.decodeBitmap(options: BitmapFactory.Options): Bitmap? {
return inputStream().use {
BitmapFactory.decodeStream(it, null, options)
}
}
@Throws(IOException::class)
fun File.decodeBitmapAtLeast(
@androidx.annotation.IntRange(from = 1) width: Int,
@androidx.annotation.IntRange(from = 1) height: Int
): Bitmap? {
val options = BitmapFactory.Options()
options.inJustDecodeBounds = true
decodeBitmap(options)
val ow = options.outWidth
val oh = options.outHeight
if (ow == -1 || oh == -1) return null
val w = ow / width
val h = oh / height
if (w > 1 && h > 1) {
val p = 31 - maxOf(Integer.numberOfLeadingZeros(w), Integer.numberOfLeadingZeros(h))
options.inSampleSize = 1 shl maxOf(0, p)
}
options.inJustDecodeBounds = false
return decodeBitmap(options)
}
